Electrochemical machining (ECM) is a well known process for machining metallic based workparts and in the past has been employed to machine complex airfoil shapes on individual blades and complex airfoil blades attached to a central cylindrical hub and extending radially therefrom around its periphery.
ECM apparatus for machining individual airfoils projecting from the central hub of an integral bladed gas turbine engine rotor or wheel is shown in the Stark et al U.S. Pat. No. 3,523,876 issued Aug. 11, 1970; the Stark et al U.S. Pat. 3,714,017 issued Jan 30, 1973; and the Kawafune at al U.S. Pat. No. 3,803,009 issued Apr. 9, 1974. In these patents, the airfoils are completely machined by the ECM process out of a cylindrical blank or disc of material.
The Trager U.S. Pat. No. 3,288,699 issued Nov. 29, 1966 illustrates an ECM apparatus for machining in simultaneous fashion multiple airfoils integral on a turbine wheel blank or disc wherein during axial advance of the cathode the workpart (turbine wheel blank) is rotated through a selected angle to impart a curve to the airfoils as they are formed by the cathode.
The Lucas U.S. Pat. No. 3,970,538 issued July 20, 1976 describes an ECM apparatus for machining oversize leading and trailing edges of airfoil blades integrally cast with a central hub to form an integral bladed rotor for a gas turbine engine. A special cathode structure is disclosed to ECM the leading and trailing edges.
Other prior art workers have employed ECM apparatus to machine a plurality of airfoil blades from one piece of elongated stock material or individual airfoils one at a time. For Example, the Wilson et al U.s. Pat. No. 4,256,555 issued Mar. 17, 1981 illustrates ECM'ing an individual airfoil shaped blade preform using opposed cathodes which are caused to move toward opposite sides of the blade preform by movable arms or rams on a conventional machine. In the past, a ball screw assembly driven by a servomotor has been employed to drive each ram with the cathode thereon. In the patent, the cathode rams are driven in opposed directions at a 45.degree. angle relative to the centerline of the blade. The Goodwin U.S. Pat. No. 3,309,294 issued Mar. 14, 1967 illustrates an ECM apparatus for shaping an individual metallic airfoil blade for an axial flow compressor of a gas turbine engine.
The Schrader U.S. Pat. No. 3,052,284 issued Oct. 4, 1977 illustrates an ECM apparatus for at least partially forming a plurality of airfoils in a workpart. The apparatus includes a plurality of separately movable electrodes, each pair of electrodes being movable along paths defining an acute angle relative to the sides of the workpart. The Schrader U.S. Pat. No. 4,057,475 issued Nov. 8, 1977 describes a ECM method for forming a plurality of airfoils in a single workpiece. The Schrader et al U.S. Pat. No. 4,167,462 issued Sept. 11, 1979 describes a control system for an ECM machine having a plurality of electrodes driven by a plurality of identical hydraulic pumps.
The Sanders U.S. Pat. No. 3,060,114 issued Oct. 23, 1982 discloses an ECM machine and method using a reciprocating cathode structure. The Inoue U.S. Pat. No. 4,504,721 issued Mar. 12, 1985, illustrates a multiple axes electrical discharge machine for forming a three dimensional cavity in a workpart.